The present invention relates generally to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to treat tissue in regions of the spine. The present invention also relates to the treatment of intervertebral discs, ligaments, cartilage, tendons, and other tissue within the vertebral column. The invention further relates to apparatus and methods for the inactivation of nervous tissue in and around the spine to alleviate pain associated with defects of the spine or intervertebral discs.
The major causes of persistent, often disabling, back pain are disruption of the disc annulus, chronic inflammation of the disc (e.g., herniation), or relative instability of the vertebral bodies surrounding a given disc, such as the instability that often occurs due to a degenerative disease. It is thought that discogenic pain may account for up to 85% of cases of back pain. Disc degeneration appears to be almost universal, occurring as part of the aging process. Intervertebral discs mainly function to cushion and tether the vertebrae, providing flexibility and stability to the patient's spine. Spinal discs comprise a central hydrophilic cushion, the nucleus pulposus, surrounded by a multi-layered fibrous ligament, the annulus fibrosus. As discs degenerate, they lose their water content and height, bringing the adjoining vertebrae closer together. This results in a weakening of the shock absorption properties of the disc and a narrowing of the nerve openings (foramina) of the spine which may pinch these nerves or nerve roots. This disc degeneration can eventually cause back and leg pain. Weakness in the annulus from degenerative discs or disc injury can allow fragments of nucleus pulposus from within the disc space to migrate into the spinal canal. There, displaced nucleus pulposus or protrusion of annulus fibrosus, e.g., herniation, may impinge on spinal nerve roots. The mere proximity of the nucleus pulposus or a damaged annulus to a nerve or nerve root can cause direct pressure against the nerve, resulting in pain, as well as sensory and motor deficit.
Often, inflammation from disc herniation can be treated successfully by non-surgical means, such as rest, therapeutic exercise, oral anti-inflammatory medications or epidural injection of corticosteroids. In some cases, the disc tissue is irreparably damaged, thereby necessitating removal of a portion of the disc or the entire disc to eliminate the source of inflammation and pressure. In more severe cases, the adjacent vertebral bodies must be stabilized following excision of the disc material to avoid recurrence of the disabling back pain. One approach to stabilizing the vertebrae, termed spinal fusion, is to insert an interbody graft or implant into the space vacated by the degenerative disc. In this procedure, a small amount of bone may be grafted and packed into the implants. This allows the bone to fuse together adjacent vertebral bodies, thereby preventing reoccurrence of the symptoms.
Until recently, spinal discectomy and fusion procedures resulted in major operations and traumatic dissection of muscle and bone removal or bone fusion. To overcome the disadvantages of traditional traumatic spine surgery, minimally invasive spine surgery was developed. In endoscopic spinal procedures, the spinal canal is not violated and therefore epidural bleeding with ensuing scarring is minimized or completely avoided. In addition, the risk of instability from ligament and bone removal is generally lower in endoscopic procedures than with open discectomy. Further, more rapid rehabilitation facilitates faster recovery and return to work.
Minimally invasive techniques for the treatment of spinal diseases or disorders include chemonucleolysis, laser techniques and mechanical techniques. These procedures generally require the surgeon to form a passage or operating corridor from the external surface of the patient to the spinal disc(s) for passage of surgical instruments, implants and the like. Typically, the formation of this operating corridor requires the removal of soft tissue, muscle or other types of tissue depending on the procedure (i.e., laparoscopic, thoracoscopic, arthroscopic, back, etc.). This tissue is usually removed with mechanical instruments, such as pituitary rongeurs, curettes, graspers, cutters, drills, microdebriders and the like. Unfortunately, these mechanical instruments greatly lengthen and increase the complexity of the procedure. In addition, these instruments sever blood vessels within this tissue, usually causing profuse bleeding that obstructs the surgeon's view of the target site.
Once the operating corridor is established, the nerve root is retracted and a portion or all of the disc is removed with mechanical instruments, such as a pituitary rongeur. In addition to the above problems with mechanical instruments, there are serious concerns because these instruments are not precise, and it is often difficult, during the procedure, to differentiate between the target disc tissue, and other structures within the spine, such as bone, cartilage, ligaments, nerves and non-target tissue. Thus, the surgeon must be extremely careful to minimize damage to the cartilage and bone within the spine, and to avoid damaging nerves, such as the spinal nerves and the dura mater surrounding the spinal cord.
Lasers were initially considered ideal for spine surgery because lasers ablate or vaporize tissue with heat, which also acts to cauterize and seal the small blood vessels in the tissue. Unfortunately, lasers are both expensive and somewhat tedious to use in these procedures. Another disadvantage with lasers is the difficulty in judging the depth of tissue ablation. Since the surgeon generally points and shoots the laser without contacting the tissue, he or she does not receive any tactile feedback to judge how deeply the laser is cutting. Because healthy tissue, bones, ligaments, and spinal nerves often lie within close proximity of the spinal disc, it is essential to maintain a minimum depth of tissue damage, which cannot always be ensured with a laser.
Monopolar radiofrequency devices have been used in limited roles in spine surgery, such as to cauterize severed vessels to improve visualization of the surgical site. These monopolar devices, however, suffer from the disadvantage that the electric current will flow through undefined paths in the patient's body, thereby increasing the risk of unwanted electrical stimulation to portions of the patient's body. In addition, since the defined path through the patient's body has a relatively high impedance (because of the large distance or resistivity of the patient's body), large voltages must typically be applied between the return and active electrodes in order to generate a current suitable for ablation or cutting of the target tissue. This current, however, may inadvertently flow along body paths having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying surrounding tissue or neighboring peripheral nerves.
Other disadvantages of conventional RF devices, particularly monopolar devices, is nerve stimulation and interference with nerve monitoring equipment in the operating room. In addition, these devices typically operate by creating a voltage difference between the active electrode and the target tissue, causing an electrical arc to form across the physical gap between the electrode and tissue. At the point of contact of the electric arcs with tissue, rapid tissue heating occurs due to high current density between the electrode and tissue. This high current density causes cellular fluids to rapidly vaporize into steam, thereby producing a “cutting effect” along the pathway of localized tissue heating. Thus, the tissue is parted along the pathway of evaporated cellular fluid, inducing undesirable collateral tissue damage in regions surrounding the target tissue site. This collateral tissue damage often causes indiscriminate destruction of tissue, resulting in the loss of the proper function of the tissue. In addition, the device does not remove any tissue directly, but rather depends on destroying a zone of tissue and allowing the body to eventually remove the destroyed tissue.
Many patients experience discogenic pain due to defects or disorders of intervertebral discs. Such disc defects include annular fissures, fragmentation of the nucleus pulposus, and contained herniation. A common cause of pain related to various disc disorders is compression of a nerve root by a distorted, bulging, or herniated disc. A posterior portion or region of the disc (corresponding to approximately the posterior one-third to one-half of the annulus fibrosus) is innervated by branches of the sinuvertebral nerve, such branches terminating in nociceptors. Stimulated nociceptors send pain messages following spinal injury or disc defects. In the case of discs having fissures, chemicals may reach nociceptors via a fissure and the chemicals may then lower the threshold for firing. In addition, pain is also caused by mechanical forces within the spine. Furthermore, it is thought that damaged or defective discs have increased innervation by branches of the sinuvertebral nerve, as compared with normal (undamaged) discs. The posterior longitudinal ligament, which is contiguous with the outer annulus, is also innervated by the sinuvertebral nerve. Thus, sensory (afferent) nerve fibers of the posterior longitudinal ligament may also be involved in back pain. There is a need for methods to treat the spine to alleviate the chronic, and often debilitating, back pain associated with innervation of the posterior of the disc and the posterior longitudinal ligament. The instant invention provides methods for decompressing nerve roots, wherein the volume of the disc is decreased. The instant invention also provides methods for electrosurgically inactivating nervous tissue within the disc and the posterior longitudinal ligament in order to alleviate back pain.